As this type of a conventional electric steering lock device, one that is disclosed in Japanese Patent Application Laid-Open Publication No. 2009-35163 (Patent Literature 1) is known. FIG. 1 shows a structure of an electric steering lock device described in Patent Literature 1. This electric steering lock device 101 is provided with a lock member 150 for prohibiting rotation of a steering shaft 180. Moreover, the lock member 150 is movably arranged between a locked position at which a tip 151a of the lock member 150 protrudes from a frame 110 and an unlocked position at which the tip 151a of the lock member 150 is accommodated inside of the frame 110. Further, the electric steering lock device 101 is provided with a cam 140 that rotates integrally with a gear wheel 132, and the lock member 150 is biased and held on a cam face 141 of the cam 140 by a biasing member (not shown). Thus, by following the rotation of the gear wheel 132, the lock member 150 moves between the locked position and the unlocked position, while sliding on the cam face 141.